1. Field of the Invention
This invention relates to a radiation image recording and read-out method and apparatus. This invention particularly relates to prevention of deterioration in image quality due to scattered radiation.
2. Description of the Prior Art
Operations for recording radiation images are carried out in various fields. For example, radiation images to be used for medical purposes are recorded as in X-ray image recording for medical diagnoses. Also, radiation images to be used for industrial purposes are recorded as in radiation image recording for non-destructive inspection of substances. In order to carry out such operations for recording radiation images, there has heretofore been utilized the so-called "radiography" in which radiation films and intensifying screens are combined with each other. With the radiography, when radiation, such as X-rays, carrying image information of an object impinges upon the intensifying screen, a fluorescent material contained in the intensifying screen absorbs energy from the radiation and produces fluorescence (i.e. instantaneously emitted light). Therefore, the radiation film, which is superposed upon the intensifying screen in close contact therewith, is exposed to the fluorescence produced by the fluorescent material, and a radiation image is thereby formed on the radiation film. In this manner, the radiation image can be directly obtained as a visible image on the radiation film.
The applicant proposed radiation image read-out apparatuses, which are referred to as the computed radiography (CR) apparatuses. With the proposed CR apparatuses, a stimulable phosphor sheet, on which a radiation image has been stored, is exposed to stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal having been obtained from the CR apparatuses is utilized for reproducing and displaying a visible image on a cathode ray tube (CRT) display device or for reproducing a visible image on film by a laser printer (LP), or the like. The reproduced image is utilized for making a diagnosis, e.g. for investigating the presence or absence of a diseased part or an injury or for ascertaining the characteristics of the diseased part or the injury.
However, in order for a radiation image to be obtained by utilizing radiation film, when the radiation image is to be visualized directly, it is necessary for sensitivity regions of the radiation film and the intensifying screen to be set so as to coincide with each other during the image recording operation. Also, it is necessary for a developing process to be carried out on the radiation film. Therefore, the problems occur in that considerable time and labor are required to obtain the radiation image by utilizing the radiation film.
Further, with the apparatuses for photoelectrically reading out a radiation image from radiation film or a stimulable phosphor sheet, the radiation image must be converted into an electric image signal, and image processing must be performed on the image signal such that a visible image having desired image density and contrast may be obtained. For such purposes, it is necessary for the scanning for reading out the radiation image to be performed by utilizing image read-out means. Therefore, operations for obtaining a visible radiation image cannot be kept simple, and considerable time is required to obtain the visible radiation image.
Such that the problems encountered with the conventional techniques may be solved, apparatuses utilizing semiconductor devices (referred to as the solid-state radiation detectors), which detect radiation and convert it into an electric signal, have been proposed. As the solid-state radiation detectors, various types of radiation detectors have been proposed. One of typical solid-state radiation detectors comprises two-dimensional image read-out means and a fluorescent material layer (i.e., a scintillator) overlaid upon the two-dimensional image read-out means. The two-dimensional image read-out means comprises an insulating substrate and a plurality of photoelectric conversion devices, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to one pixel. When the scintillator is exposed to radiation carrying image information, it converts the radiation into visible light carrying the image information. (The solid-state radiation detector having such a constitution will hereinbelow be referred to as the "photo conversion type of solid-state radiation detector.") Another typical solid-state radiation detector comprises two-dimensional image read-out means and a radio-conductive material overlaid upon the two-dimensional image read-out means. The two-dimensional image read-out means comprises an insulating substrate and a plurality of charge collecting electrodes, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to one pixel. When the radio-conductive material is exposed to radiation carrying image information, it generates electric charges carrying the image information. (The solid-state radiation detector having such a constitution will hereinbelow be referred to as the "direct conversion type of solid-state radiation detector.")
The photo conversion types of solid-state radiation detectors are described in, for example, Japanese Unexamined Patent Publication Nos. 59(1984)-211263 and 2(1990)-164067, PCT International Publication No. WO92/06501, and "Signal, Noise, and Read Out Considerations in the Development of Amorphous Silicon Photodiode Arrays for Radiotherapy and Diagnostic X-ray Imaging," L. E. Antonuk et al., University of Michigan, R. A. Street Xerox, PARC, SPIE Vol. 1443, Medical Imaging V; Image Physics (1991), pp. 108-119.
Examples of the direct conversion types of solid-state radiation detectors include the following:
(i) A solid-state radiation detector having a thickness approximately 10 times as large as the ordinary thickness, the thickness being taken in the direction along which radiation is transmitted. The solid-state radiation detector is described in, for example, "Material Parameters in Thick Hydrogenated Amorphous Silicon Radiation Detectors," Lawrence Berkeley Laboratory, University of California, Berkeley, Calif. 94720 Xerox Parc. Palo Alto. Calif. 94304. PA1 (ii) A solid-state radiation detector comprising two or more layers overlaid via a metal plate with respect to the direction along which radiation is transmitted. The solid-state radiation detector is described in, for example, "Metal/Amorphous Silicon Multilayer Radiation Detectors, IEE TRANSACTIONS ON NUCLEAR SCIENCE, Vol. 36, No. 2, April 1989. PA1 (iii) A solid-state radiation detector utilizing CdTe, or the like. The solid-state radiation detector is proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-216290. PA1 i) a first electrical conductor layer having permeability to recording radiation, PA1 ii) a recording photo-conductive layer, which exhibits photo-conductivity when it is exposed to the recording radiation having passed through the first electrical conductor layer, PA1 iii) a charge transporting layer, which acts approximately as an insulator with respect to electric charges having a polarity identical with the polarity of electric charges occurring in the first electrical conductor layer, and which acts approximately as a conductor with respect to electric charges having a polarity opposite to the polarity of the electric charges occurring in the first electrical conductor layer, PA1 iv) a reading photo-conductive layer, which exhibits photo-conductivity when it is exposed to a reading electromagnetic wave, and PA1 v) a second electrical conductor layer having permeability to the reading electromagnetic wave, PA1 the layers being overlaid in this order. PA1 i) locating a radiation source, which produces radiation, on one side of an object, PA1 ii) locating two-dimensional image read-out means on the other side of the object, the two-dimensional image read-out means comprising stripe-shaped electrodes for reading latent image charges, which carry image information, and PA1 iii) performing an operation for recording and reading out a radiation image of the object, PA1 wherein a grid plate is located between the object and the two-dimensional image read-out means, the grid plate guiding only the radiation, which comes from a specific direction, to the two-dimensional image read-out means, and PA1 the operation for recording and reading out the radiation image of the object is performed in this state. PA1 i) a radiation source, which produces radiation, PA1 ii) two-dimensional image read-out means comprising stripe-shaped electrodes for reading latent image charges, which carry image information, and PA1 iii) a grid plate, which is located between the radiation source and the two-dimensional image read-out means, the grid plate guiding only the radiation, which comes from a specific direction, to the two-dimensional image read-out means. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in the direction approximately normal to the longitudinal direction of each stripe-shaped electrode, (i.e., the stripe-shaped electrodes and the radiation absorbing substance regions of the grid plate are arrayed in parallel with each other) and PA1 a spatial frequency fC of the pitch of the stripe-shaped electrodes is at least two times as high as a spatial frequency fG of the grid pitch. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in the longitudinal direction of each stripe-shaped electrode, (i.e., the stripe-shaped electrodes and the radiation absorbing substance regions of the grid plate are arrayed so as to intersect perpendicularly to each other) and PA1 a spatial frequency fS of a sampling pitch, at which the latent image charges are read with scanning in the longitudinal direction of each stripe-shaped electrode, is at least two times as high as a spatial frequency fG of the grid pitch. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in the direction approximately normal to the longitudinal direction of each stripe-shaped electrode, (i.e., the stripe-shaped electrodes and the radiation absorbing substance regions of the grid plate are arrayed in parallel with each other) and PA1 a difference between a spatial frequency fC of the pitch of the stripe-shaped electrodes and a spatial frequency fG of the grid pitch is at least 1 cycle/mm. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in the longitudinal direction of each stripe-shaped electrode, (i.e., the stripe-shaped electrodes and the radiation absorbing substance regions of the grid plate are arrayed so as to intersect perpendicularly to each other) and PA1 a difference between a spatial frequency fS of a sampling pitch, at which the latent image charges are read with scanning in the longitudinal direction of each stripe-shaped electrode, and a spatial frequency fG of the grid pitch is at least 1 cycle/mm. PA1 i) locating a radiation source, which produces radiation, on one side of an object, PA1 ii) locating two-dimensional image read-out means and a radio-conductive material, which is formed on the two-dimensional image read-out means, on the other side of the object, the two-dimensional image read-out means comprising an insulating substrate and a plurality of charge collecting electrodes, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to a single pixel, the radio-conductive material generating electric charges carrying image information when it is exposed to radiation carrying the image information, and PA1 iii) performing an operation for recording and reading out a radiation image of the object, PA1 wherein a grid plate is located between the object and the radio-conductive material, the grid plate guiding only the radiation, which comes from a specific direction, to the radio-conductive material, and PA1 the operation for recording and reading out the radiation image of the object is performed in this state. PA1 i) a radiation source, which produces radiation, PA1 ii) two-dimensional image read-out means comprising an insulating substrate and a plurality of charge collecting electrodes, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to a single pixel, PA1 iii) a radio-conductive material, which is formed on the two-dimensional image read-out means, the radio-conductive material generating electric charges carrying image information when it is exposed to radiation carrying the image information, and PA1 iv) a grid plate, which is located between the radiation source and the radio-conductive material, the grid plate guiding only the radiation, which comes from a specific direction, to the radio-conductive material. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in at least either one of the X direction and the Y direction, and PA1 a spatial frequency fD of the charge collecting electrodes in the grid array direction is at least two times as high as a spatial frequency fG of the grid pitch. PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in at least either one of the X direction and the Y direction, and PA1 a difference between a spatial frequency fD of the charge collecting electrodes in the grid array direction and a spatial frequency fG of the grid pitch is at least 1 cycle/mm. PA1 i) a radiation source, which produces radiation, PA1 ii) two-dimensional image read-out means comprising an insulating substrate and a plurality of photoelectric conversion devices, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to a single pixel, PA1 iii) a fluorescent material, which is formed on the two-dimensional image read-out means, the fluorescent material converting radiation carrying image information into visible light carrying the image information when it is exposed to the radiation carrying the image information, and PA1 iv) a grid plate, which is located between the radiation source and the fluorescent material, the grid plate guiding only the radiation, which comes from a specific direction, to the fluorescent material, PA1 wherein the photoelectric conversion devices of the two-dimensional image read-out means are arrayed at a predetermined pitch in an X direction and at a predetermined pitch in a Y direction, PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in at least either one of the X direction and the Y direction, and PA1 a spatial frequency fP of the photoelectric conversion devices in the grid array direction is at least two times as high as a spatial frequency fG of the grid pitch. PA1 i) a radiation source, which produces radiation, PA1 ii) two-dimensional image read-out means comprising an insulating substrate and a plurality of photoelectric conversion devices, which are formed in a two-dimensional pattern on the insulating substrate and each of which corresponds to a single pixel, PA1 iii) a fluorescent material, which is formed on the two-dimensional image read-out means, the fluorescent material converting radiation carrying image information into visible light carrying the image information when it is exposed to the radiation carrying the image information, and PA1 iv) a grid plate, which is located between the radiation source and the fluorescent material, the grid plate guiding only the radiation, which comes from a specific direction, to the fluorescent material, PA1 wherein the photoelectric conversion devices of the two-dimensional image read-out means are arrayed at a predetermined pitch in an X direction and at a predetermined pitch in a Y direction, PA1 the grid plate is constituted of radiation absorbing substance regions and radiation-permeable substance regions, which are arrayed alternately at a predetermined grid pitch so as to stand side by side in at least either one of the X direction and the Y direction, and PA1 a difference between a spatial frequency fP of the photoelectric conversion devices in the grid array direction and a spatial frequency fG of the grid pitch is at least 1 cycle/mm. PA1 a) a first thin metal film layer, which acts as a lower electrode, PA1 b) an amorphous silicon nitride insulation layer (a-SiN.sub.x), which blocks passage of electrons and holes, PA1 c) a hydrogenated amorphous silicon photoelectric conversion layer (a-Si:H), PA1 d) an injection blocking layer selected from the group consisting of an n-type injection blocking layer, which blocks injection of hole carriers, and a p-type injection blocking layer, which blocks injection of electron carriers, and PA1 e) a layer selected from the group consisting of a transparent electrode layer, which acts as an upper electrode, and a second thin metal film layer, which is formed on a portion of the injection blocking layer, PA1 the layers being overlaid in this order on the insulating substrate. PA1 the first image processing means performs processing for suppressing the signal components SG, which carry the spatial frequency fG of the grid pitch, on the digital image signal, or the second image processing means performs processing for suppressing the signal components SM, which carry the moire frequency occurring due to the grid, on the digital image signal. PA1 a) the first thin metal film layer, which acts as the lower electrode, PA1 b) the amorphous silicon nitride insulation layer (a-SiN.sub.x), which blocks passage of electrons and holes, PA1 c) the hydrogenated amorphous silicon photoelectric conversion layer (a-Si:H), PA1 d) the injection blocking layer selected from the group consisting of the n-type injection blocking layer, which blocks injection of hole carriers, and the p-type injection blocking layer, which blocks injection of electron carriers, and PA1 e) the layer selected from the group consisting of the transparent electrode layer, which acts as the upper electrode, and the second thin metal film layer, which is formed on a portion of the injection blocking layer, PA1 the layers being overlaid in this order on the insulating substrate.
Also, in Japanese Patent Application No. 9(1997)-222114, the applicant proposed a solid-state radiation detector improved over the direct conversion type of solid-state radiation detector. (The proposed solid-state radiation detector will hereinbelow be referred to as the "improved direct conversion type of solid-state radiation detector.")
The improved direct conversion type of solid-state radiation detector comprises:
In the improved direct conversion type of solid-state radiation detector, latent image charges carrying image information are accumulated at an interface between the recording photo-conductive layer and the charge transporting layer.
In the improved direct conversion type of solid-state radiation detector, the latent image charges may be read with a technique, wherein the second electrical conductor layer (i.e., a reading electrode) is constituted of a flat plate-shaped electrode, and the reading electrode is scanned with spot-like reading light, such as a laser beam, the latent image charges being thereby detected. Alternatively, the latent image charges may be read with a technique, wherein the reading electrode is constituted of comb tooth-shaped electrodes (i.e., stripe-shaped electrodes), and the stripe-shaped electrodes are scanned with light, which is produced by a line light source extending along a direction approximately normal to the longitudinal direction of each stripe-shaped electrode, and in the longitudinal direction of each stripe-shaped electrode, the latent image charges being thereby detected.
An image signal, which has been obtained from one of various types of solid-state radiation detectors described above, is amplified by an amplifier of the solid-state radiation detector. The amplified image signal is then subjected to predetermined image processing and used for reproducing a visible image on image reproducing means, such as a cathode ray tube (CRT) display device. With such solid-state radiation detectors, a visible radiation image of an object can be reproduced immediately in a real time mode and without complicated operations being required. Therefore, the problems encountered with the aforesaid apparatuses utilizing radiation film, or the like, can be eliminated.
With each of the radiation image recording and read-out apparatuses utilizing various types of solid-state radiation detectors described above, in cases where a radiation image of an object is to be read out with the solid-state radiation detector, radiation having been produced by a radiation source is irradiated to the object, and the radiation carrying image information of the object is detected by the solid-state radiation detector.
However, the radiation is scattered to various directions in the object, and signal components caused to occur by the scattered radiation mix in the image signal, which carries the image information of the object. Therefore, the problems occur in that a sufficiently high signal-to-noise ratio cannot be obtained, or high resolution cannot be obtained. As a result, a visible image having good image quality cannot be obtained.